The present invention relates, in general, to a gas burner used for applying labels to plastic bottles or containers and, more particularly, to a concentrator that is attachable to the burner so as to direct the burner flame toward the container to be labeled and minimize the infrared radiation therefrom.
Plastics, as well as some other materials, benefit from a surface treatment that improves bonding between the surface to be labeled and an adhesive backed label. In the plastic container industry, this surface treatment is sometimes referred to as oxidation. The most common form of container oxidation utilizes a flame formed from a flammable gas/air mixture emanating from a gas/air burner. The container to be labeled is moved past the flame emanating from the burner causing the material comprising the container to be heated. Exposure to the flame oxidizes, i.e., alters the surface tension, of the plastic container so that the label can be applied to same. One of the disadvantages of this process is that the flame produces heat within the plastic container which might cause the container to distort if it has very thin walls. In addition, if the plastic material has a low melting temperature, the container may melt. It should be noted that the flame produced by a burner generates heat that is radiated in all directions. Some of this heat is stored in the burner body and radiates outwardly in the form of infrared radiation. Thus, a container to be labeled is exposed to infrared radiation as it is approaching the burner, direct heat when it passes in front of the burner, and additional infrared radiation as it moves away from the burner. In view of the foregoing, the total heat gain within the container during this process can be substantial.
The foregoing process can also be used as a post-treatment method for labeled containers. In the post-treatment method, sufficient heat is applied to the labeled containers to cause a wax substance to flow over the label and act as an overlay thereon. The wax forms a protective barrier between the environment and the label. In the post-treatment method, sufficient heat energy must be provided in order to cause the wax to flow over the label without distorting or melting the container.
It has been found that the foregoing process cannot be used effectively for thin walled plastic containers or plastic containers formed from a material having a low melting temperature. The flame pattern produced by presently available burners is relatively wide resulting in such containers absorbing too much heat and infrared radiation causing the containers to distort or melt. Shielding the sides of the burner does not sufficiently reduce the infrared radiation reaching the containers.
In view of the foregoing, it has become desirable to develop a concentrator that can be attached to the outlet of a burner so as to concentrate the flame produced by same on the container being labeled and which significantly reduces the amount of infrared radiation therefrom.
The present invention solves the problems associated with prior art burners, and other problems, by providing a funnel-shaped concentrator that is attachable to the outlet of a standard cast iron burner. The concentrator directs the flame produced by the burner toward the outlet slit in the concentrator causing the flame emanating from the outlet slit to be directed toward the container being labeled. One or more layers of refractory insulating material are placed along the sides of the concentrator, the body of burner and the top and bottom surfaces of the concentrator so as to minimize the amount of infrared radiation emanating therefrom. In this manner, the containers being labeled or on which a label has been affixed are exposed only to the flame being directed outwardly from the outlet slit in the concentrator. Thus, the amount of infrared radiation to which the containers are exposed prior to or after being labeled is greatly reduced permitting containers having thin walls or formed from materials having a low melting temperature to be labeled.